Interpretive Summary: Approximately 80% of the tall fescue pastures in the southeastern and midwestern United States are infested with a fungus called Neotyphodium coenophialum. The fungus seems to help the plant be more tolerant of drought conditions and to help protect it from some pests. However, the fungus can have adverse effects on cattle that graze fescue pastures infested with the fungus. The fungus appears to decrease animal performanc and decrease the animals heat tolerance. Some breeds (Brahman for example) seem to be more tolerant of the fungus. Typical visual symptoms of the fungus in cattle are a shaggy, muddy hair coat. The effects of the fungus on the health and performance of cattle shipped and fed in feedlots was not known. Therefore, these three experiments were conducted to determine the influence of the concentration of the endophytic fungus infestation in tall fescue pastures and calf genotype on the subsequent health and performance of steers in the feedlot. In all experiments steers grazed fescue pasture in Georgia, then were transported 1,600 km to Texas and finished on a 93% concentrate diet. The results indicated that cattle from fescue pastures infested with the fungus had better performance than cattle from "clean" pastures. This was probably a compensatory gain response. Results of these studies are interpreted to indicate that the adverse effects of high-fungus infestations in fescue pastures can carry-over to the feedlot for approximately 14 d. However, steers from highly infested pastures can compensate for poor pasture performance with improved performance in the feedlot when no adverse health effects occur. Any impact of the fungus seems to be similar in Brahman-cross and Angus steers.

Technical Abstract:
Three experiments were conducted to determine the influence of the endophytic fungus in tall fescue pastures and calf genotype on the performance of steers in the feedlot. In Exp.1 and 2, Angus steers grazed fescue pastures in Georgia containing low-, moderate-, or high-endophyte infestations. Steers were transported to Texas in October (Exp. 1) and July (Exp. 2), fed a 93% concentrate diet, and slaughtered at a backfat thickness of 12 mm. In both trials, dry matter intake and carcass characteristics were not affected (P>0.05) by endophyte infestation. Feedlot ADG and gain:feed increased as the previous pasture endophyte infestation increased (P<0.05). Serum cholesterol concentrations tended (P<0.10) to decrease with increasing endophyte infestation. In Exp. 3, Angus and Brahman x British crossbred steers grazed fescue pastures in Georgia containing low-, moderate-, or high-endophyte. Steers were transported to Texas in late August and fed a finishing diet. As endophyte infestation increased, serum urea N concentrations and gain:feed ratios increased (P<0.05), whereas initial BW, transit shrink (kg), serum cholesterol concentrations, final BW, and carcass weights decreased (P<0.05) in both breed groups. As endophyte infestation increased, arrival rectal temperatures increased (P<0.05) in Angus steers but not in Brahman- cross steers. Results of these studies are interpreted to indicate that the adverse effects of high-endophyte infestations in fescue pastures can carry-over to the feedlot for approximately 14 d. However, steers from infested pastures can compensate for poor pasture performance with improved performance in the feedlot when no adverse health effects occur. Any impact of the endophyte seems to be similar in Brahman-cross and Angus steers.